742 citations · 10.2k across the 143 of their papers we have counts for
22 papers · 1 filter
Alfvén QPOs in Magnetars
Hajime Sotani, Kostas Kokkotas, Nikolaos Stergioulas
We investigate torsional Alfvén oscillations of relativistic stars with a global dipole magnetic field, via two-dimensional numerical simulations. We find that a) there exist two f…
Torsional Oscillations of Relativistic Stars with Dipole Magnetic Fields II. Global Alfvén Modes
H. Sotani, K. D. Kokkotas, N. Stergioulas +1
We investigate torsional Alfvén modes of relativistic stars with a global dipole magnetic field. It has been noted recently (Glampedakis et al. 2006) that such oscillation modes co…
Non-axisymmetric instability and fragmentation of general relativistic quasi-toroidal stars
Burkhard Zink, Nikolaos Stergioulas, Ian Hawke +3
In a recent publication, we have demonstrated that differentially rotating stars admit new channels of black hole formation via fragmentation instabilities. Since a higher order in…
Torsional Oscillations of Relativistic Stars with Dipole Magnetic Fields
H. Sotani, K. D. Kokkotas, N. Stergioulas
We present the formalism and numerical results for torsional oscillations of relativistic stars endowed with a strong dipole magnetic field. We do a systematic search of parameter…
Non-linear axisymmetric pulsations of rotating relativistic stars in the conformal flatness approximation
Harald Dimmelmeier, Nikolaos Stergioulas, Jose A. Font
We study non-linear axisymmetric pulsations of rotating relativistic stars using a general relativistic hydrodynamics code under the assumption of a conformal flatness. We compare…
Nonlinear Pulsations in Differentially Rotating Neutron Stars: Mass-Shedding-Induced Damping and Splitting of the Fundamental Mode
Nikolaos Stergioulas, Theocharis A. Apostolatos, Jose A. Font
We study small-amplitude, nonlinear pulsations of uniformly and differentially rotating neutron stars employing a two-dimensional evolution code for general-relativistic hydrodynam…
Non-linear resonance in the accretion disk of a millisecond pulsar
Wlodek Kluzniak, Marek A. Abramowicz, Shoji Kato +2
Twin quasi-periodic millisecond modulations of the X-ray flux (kHz QPOs) have recently been reported from an accreting 2.5 ms X-ray pulsar. We identify modes of disk oscillations w…
An unusually low mass of some "neutron" stars?
D. Gondek-Rosinska, W. Kluzniak, N. Stergioulas
The X-ray emission of RXJ1856.5-3754 has been found to coincide to unprecedented accuracy with that of a blackbody, of radius 5.8+-0.9 km for the measured parallax distance of 140…
Spin-down of Relativistic Stars with Phase Transitions and PSR J0537-6910
N. K. Spyrou, N. Stergioulas
Using a highly accurate numerical code, we study the spin down of rotating relativistic stars, undergoing a quark deconfinement phase transition. Such phase transitions have been s…
Time evolution of the linear perturbations of a rotating Newtonian polytrope
D. I. Jones, N. Andersson, N. Stergioulas
We present the results of numerical time evolutions of the linearised perturbations of rapidly and rigidly rotating Newtonian polytropes while making the Cowling approximation. The…
Lower limits on the maximum orbital frequency around rotating strange stars
D. Gondek-Rosinska, N. Stergioulas, T. Bulik +2
Observations of kHz quasi-periodic oscillations (QPOs) in the X-ray fluxes of low-mass X-ray binaries (LMXBs) have been used in attempts to constrain the external metric of the com…
Fast Magnetosonic Waves Driven by Gravitational Waves
D. Papadopoulos, N. Stergioulas, L. Vlahos +1
The propagation of a gravitational wave (GW) through a magnetized plasma is considered. In particular, we study the excitation of fast magnetosonic waves (MSW) by a gravitational w…
Torsional Oscillations of Magnetized Relativistic Stars
Neophytos Messios, Demetrios B. Papadopoulos, Nikolaos Stergioulas
Strong magnetic fields in relativistic stars can be a cause of crust fracturing, resulting in the excitation of global torsional oscillations. Such oscillations could become observ…
Axisymmetric Modes of Rotating Relativistic Stars in the Cowling Approximation
Jose A. Font, Harald Dimmelmeier, Anshu Gupta +1
Axisymmetric pulsations of rotating neutron stars can be excited in several scenarios, such as core-collapse, crust and core-quakes and binary mergers and could become detectable e…
Nonlinear evolution of r-modes in rotating relativistic stars
Jose A. Font, Nikolaos Stergioulas
A numerical study of nonlinear r-modes in isentropic, rapidly rotating relativistic stars, via 3-D general-relativistic hydrodynamical evolutions, is presented. On dynamical timesc…
Evolutionary Self-Energy-Loss Effects in Compact Binary Systems: Importance of Rapid Rotation and of Equation of State
N. K. Spyrou, N. Stergioulas
The spin-down of a millisecond pulsar in a compact binary system leads to self-energy losses, that cause the binary's orbital period to increase (the effect being of first post-New…
R-mode runaway and rapidly rotating neutron stars
N. Andersson, D. I. Jones, K. D. Kokkotas +1
We present a simple spin evolution model that predicts that rapidly rotating accreting neutron stars will mainly be confined to a narrow range of spin-frequencies; P= 1.5-5 ms. Thi…
Keplerian frequencies and innermost stable circular orbits of rapidly rotating strange stars
N. Stergioulas, W. Kluzniak, T. Bulik
It has been suggested that the frequency in the co-rotating innermost stable circular orbit (ISCO) about a compact stellar remnant can be determined through X-ray observations of l…
On the relevance of the r-mode instability for accreting neutron stars and white dwarfs
Nils Andersson, Kostas D. Kokkotas, Nikolaos Stergioulas
We present a case study for the relevance of the r-mode instability for accreting compact stars. Our estimates are based on approximations that facilitate back-of-the-envelope calc…
Analytic description of the r-mode instability in uniform density stars
K. D. Kokkotas, N. Stergioulas
We present an analytic description of the -mode instability in newly-born neutron stars, using the approximation of uniform density. Our computation is consistently accurate to…
Upper Limit Set by Causality on the Rotation and Mass of Uniformly Rotating Relativistic Stars
Scott Koranda, Nikolaos Stergioulas, John L. Friedman
Causality alone suffices to set a lower bound on the period of rotation of relativistic stars as a function of their maximum observed mass. That is, by assuming a one-parameter equ…
Comparing Models of Rapidly Rotating Relativistic Stars Constructed by Two Numerical Methods
Nikolaos Stergioulas, John L. Friedman
We present the first direct comparison of codes based on two different numerical methods for constructing rapidly rotating relativistic stars. A code based on the Komatsu-Eriguchi-…